NMR studies of tautomerism in the fungal melanin biosynthesis intermediate 1,3,8-trihydroxynaphthalene

Abstract

The naphthol reductase catalysed conversion of 1,3,8-trihydroxynaphthalene (T₃HN) to vermelone has been studied using a partially purified cell-free enzyme preparation from Verticillium dahliae. NMR studies show that in aqueous buffer T₃HN exists as an equilibrium mixture of the parent phenol and a keto-tautomer. 1,3,6,8-Tetrahydroxynaphthalene (T₄HN) is a more efficient substrate than T₃HN for the naphthol reductase. 1,3-Dihydroxynaphthalene also acts as a substrate and is converted to 8-deoxyvermelone.